On Nov 6, 2012, at 5:42 PM, John Anderson wrote:
> I have a mixin that declares a primary key but would like to dynamically
> override the name of it.
>
> So for instance this is the base:
>
> class BaseModel(object):
> @declared_attr
> def pk(self):
> return sa.Column(sa.Integer, autoincrement=True, primary_key=True)
>
> but in some circumstances people want to use my mixin but declare the primary
> key property as id instead.
>
> So I want to be able to do something class
>
> class SubClass(BaseModel):
> _idAttribute = 'id'
>
> and have it use id in the database and has the class property to reference
> instead of pk.
>
>
> Is this possible?
The name assigned to the class and the name given to the Column when it emits
CREATE TABLE are two different things.
The "name" is what you'll see in CREATE TABLE, easy enough, "return
Column('id', ...)"
As far as the name assigned to the class, in classical mappings the "key" of
the Column is used, and it might be nice if declarative looked at column.key in
this case, however it doesn't. There is a way this could probably be hacked
on, by creating a custom __mapper__ classmethod and converting all the Columns
with custom .keys to be mapped with that name. a little ugly, though.
of course the blunt tool that works in all cases is the custom metaclass, but
that approach is fairly tedious and is probably a lot uglier than just the
__mapper__ hack above.
Another way that is a little verbose but is the least intrusive is to just use
more @declared_attrs.
in 0.8, @declared_attr can be specified on a non-mixin, so this works there:
class A(BaseModel, Base):
__tablename__ = "a"
@declared_attr
def pk(self):
return None
@declared_attr
def id(self):
return BaseModel.pk
if 0.7, another mixin can do it:
class SubBaseModel(BaseModel):
@declared_attr
def pk(self):
return None
@declared_attr
def id(self):
return BaseModel.pk
class A(SubBaseModel, Base):
__tablename__ = "a"
i can show you the __mapper__ hack if that's not good enough.
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